This invention relates to a new method to coat metals, metal oxides, or metal alloys onto solid polymer electrolytes or other ion-conducting polymer surfaces. Materials prepared using this method would gain advantage in electrochemical and membrane-based applications. By employing dual ion-beam assisted deposition (IBAD), one can systematically prepare consistent thin films of these metals on solid polymer electrolyte membranes such as Nafion.RTM. (DuPont, Wilmington, Del.), a copolymer of tetrafluoroethylene and sulfonyl fluoride vinyl ether and the membranes coated thereby and electrolytic cells containing the same.